High-temperature seals

ABSTRACT

Seals for high-temperature applications have a composite construction including a resilient fibrous ceramic backing layer and a hard surface layer of metal or ceramic supported by the backing layer and providing a sealing face for rubbing contact with the part to be sealed against. Various methods of construction of such seals are described and an arrangement is disclosed in which the density of the backing layer is varied across its thickness to achieve an optimum combination of resiliency with suitable supporting characteristics for the surface layer.

United States Patent Inventors Waldemarliryniszak Cullercoats, NorthShields; Robert Porteous Graham, Durham City, both of England Appl. No.819,547 Filed Apr. 28, 1969 Patented Jan. 11, 1972 Assignee Clarke,Chapman & Co. Limited Gateshead, Durham County, England Priority Apr.29, 1968 Great Britain 20,296/68 HIGH-TEMPERATURE SEALS 12 Claims, 9Drawing Figs.

11.8. CI 277/96, 165/9 Int. Cl. F16j 15/16 Field 01' Search 277/96, 227,228, 231, 235, 235 A, 235 B, 236, 234, 81; 165/9 References Cited UNITEDSTATES PATENTS 9/1962 Daunt et al. 277/81 Primary Examiner-Herbert F.Ross Assistant Examiner- Robert 1. Smith Attorney-Jacies and GreensideABSTRACT: Seals for high-temperature applications have a compositeconstruction including a resilient fibrous ceramic backing layer and ahard surface layer of metal or ceramic supported by the backing layerand providing a sealing face for rubbing contact with the part to besealed against. Various methods of construction of such seals aredescribed and an arrangement is disclosed in which the density of thebacking layer is varied across its thickness to achieve an optimumcombination of resiliency with suitable supporting-characteristics forthe surface layer.

HIGH-TEMPERATURE SEALS This invention relates to seals for use betweenmoving members and capable of operation at relatively high temperatures.

In many applications in engineering it is necessary to provide sealswhich are in sliding engagement with a moving member and which have tooperate in a high-temperature environment. In rotary regenerative heatexchangers, for example, a disc or cylindrical drum-type rotor rotatesin a stator casing passing alternately through hot fluid and cold fluidcompartments in the casing.- Where the fluids are at diflerent pressuresit is necessary to have seals engaging the rotor to seal against leakageover the rotor surface between the different compartments.

Differential expansion can result in dimensional changes which reducethe efficiency of the seals and generally speaking the ideal seal forsuch purposes is one which has sufficient flexibility to enable it toadjust to dimensional changes while at the same time having hard wearingand low-friction properties in unlubricated rubbing contact.

A seal according to the invention has a composite constructioncomprising a surface element providing a face for a sliding seal and afibrous backing element supporting said surface element.

In two possible arrangements according to the invention, the surfaceelement may be formed by deposition onto a face of the fibrous backingelement or the fibrous element may form a resilient housing receiving aseparately formed sealing element.

The fibrous backing element is preferably of a ceramic nature, that isto say, of a refractory, high-temperature and/or corrosion resistantnonmetallic material, the fibers being held together with a suitablebinder.

The density of the fibrous backing element may be uniform throughout ormay vary from a maximum value adjacent to the sealing surface to aminimum value remote from the sealing surface. The density may be variedby building up the backing element in layers, each layer being formedwith a binder of different concentration from that of the other layers.

Various embodiments of the invention are illustrated by way of examplesin the accompanying drawings in which:

FIGS. 1 to 5 are transverse sections through alternative seals inaccordance with the invention,

FIG. 6 is a view in the direction of arrow A in FIG. 5,

FIG. 7a is a section through a mould for forming fibrous backing elementfor a seal such as that in FIG. 1,

FIG. 7b being an illustration of the seal produced by the mould in planview, and

FIG. 8 shows a transverse section of a seal according to the inventionin which the fibrous backing element has a varying density.

Referring first to FIG. 1, the seal comprises a fibrous backing elementIn and a wear resistant surface element 2a of low friction properties.The seal is located in a housing 3 of one of the members to be sealed.

In FIG. 2 the fibrous backing element is in the form of a shoe 1breceiving the surface element 2b in a recess. In an alternative form(FIG. 3) a housing 3 forms a channel and the backing element 10 supportsa metal surface element 2c that has been formed separate from thebacking element. The surface element may itself provide the sealing faceor it may have a surface layer 2c that takes the rubbing contact for theseal.

In the embodiment of FIG. 4 the surface element comprises a metal member2d which has lugs 4a with intumed lips 5a fitting into recesses in thesides of the fibrous backing element Id.

In the embodiment shown in FIGS. 5 and 6, the surface element is formedby a metal member 22 which, with the fibrous element le, is located in ahousing 3a. The housing 3a has slots 6 in which seat lugs 4b on themember 2e. The transverse sectional width of the backing element and themain part of the surface element is less than that of the housing 3abutoutturned lips 5b on the lugs 4b increase the overall width to thatof the housing.

The fibrous backing element can be made from ceramic fibrous materialssuch as alumino-silicate, chrome stabilized alumino-silicate, carbonfiber (i.e. carbon-fiber blanket). boron nitride etc. manufactured inthe form of paper, blanket or bulk fiber.

To form the backing element a bulk fiber mass or sheets of fibrousmaterial cut to the profile of the seal are soaked in a bath containinga liquid binder such as silicon ester or colloidal silica. On removalfrom the bath the material is lightly pressed to remove surplus binderand then placed in a mould 14 (see FIG. 7) that has been suitablytreated with a coating of a material such as polytetrafluorethylene tofacilitate subsequent removal of the backing element from the mould.Several layers of the fibrous material may be laid in the mould before aclosing member 15 is fitted and compression applied to the material togive the desired thickness and density. The material is left in themould until completely dry, for example 2 to 3 days of air drying or 4to 6 hours if oven drying at temperatures up to F. On removal from themould, the backing element is lightly fettled and in order to preventspalling is is coated with undiluted liquid hinder or a fine meshcoating cement. In FIG. 7 the backing element is in the form of an innerand outer ring of material joined by radial spokes, not shown.

In many applications it is preferably to vary the density of the fibrousbacking element. This can be achieved by forming the element in severallayers as indicated at l, 1" etc., in FIG. 8, and increasing thedilution of the binder (e.g., from nil dilution to 50 percent dilution)for successive layers. The laminations may be compressed in a singlemoulding operation or each may be allowed to dry out partly undercompression before a further lamination is added.

A graded density arrangement is helpful if the surface element is formedby flame or plasma spraying since unless the surface being treated isrigid and sufficiently uniform it can be damaged in the process. Byvariation of the density of the backing element, a suitably rigidsurface is provided for the spraying process without sacrificing theresiliency required in the finished seal.

The surface element 2 can be produced in a number of ways. These includeflame or plasma spraying of the fibrous backing element with a hard facemetal or a ceramic, or producing the element in a solid hard face metalor ceramic as in the case of elements 2b or 2c. Another way is to flameor plasma spray the face material onto a metal former, such as themembers 2d and 2e, which is mounted on the fibrous backing elementeither integrally on the substrate or simply supported thereon.

In all cases it is desirable to achieve the finest possible surfacefinish by grinding and lapping the sealing face and it will, of course,be required to ensure that the rotor face with which the seal engageshas a similarly high standard finish. If the surface element is of metalit can be further coated with a material having low friction propertiesif so desired.

If a sprayed surface element is to be formed, the backing element can bemounted on a mandrel and rotated while the spray coating is deposited tothe desired thickness. Obviously the temperature and fluid environmentof the seal in operation, in addition to the material type of the rotoror other member that it rubs upon, will in many cases dictate thecoating material which must be employed. Simply as'examples from therange of available materials there can be mentioned Cr O;;+TiOAigOgFl'TiOgI Nigozvl Algoztl Zl'OgZ Cr O Cr3C WC: et. In theapplication of a coating care must be exercised to avoid overheating ofthe substrate and also to ensure an even deposit buildup. On completionof the coating process, the seal is ground on the mandrel then removedfor final lapping.

"Whi'the seams daeererheiaeraerafinc surface element, this may beprepared separately from the backing element, if required with spraydeposition of a sealing layer as referred to above, before bonding tothe backing element using, e.g., a sodium silicate solution.Alternatively, the surface element can be secured to the backing elementby being placed in the mould with the fibrous material.

The completed seal may be mounted in a shoe or housing (not shown) ofthe structure in which it is to be employed and which will provide bothlocation and lateral support for the seal.

Seals made in the manner described above possess a degree of resilience,can be moulded to a variety of shapes and, being principally made of lowbulk density ceramic materials possess good thermal shock resistance andlow thermal conductivity, while they can be designed to function at hightemperature, for example up to 650 C. and above when used with rotaryregenerative heat exchangers, without recourse to cooling systems.

What we claim and desire to secure by Letters Patent is:

l. A seal comprising, in combination, a surface element, a face of saidelement forming a sliding seal face, and an internal resilient fibrousbacking element permanently attached to an opposed face of the surfaceelement and supporting said surface element, said backing element beingprincipally composed of low bulk density fibrous materials.

2. A seal according to claim 1 wherein the backing element has a densitythat varies with the distance from the surface element, the region ofgreatest density being closest to the surface element.

3. A seal according to claim 1 wherein the surface element comprises ametal member formed separately from the backing element.

4. A sea] according to claim 1 wherein auxiliary location pieces areprovided on the surface element, said pieces projecting away from thesealing face to engage the backing element so as to prevent relativemovement between the surface and backing elements in a plane parallel tothe sealing face.

5. A seal according to claim 4 wherein said location pieces lie onopposite side edges of the backing element section, an inwardly directedlip on at least one piece projecting into its associated backing elementside edge.

6. A seal according to claim 4 wherein a housing or support meanscarries the surface and backing elements, said means having a sectionalwidth greater than the backing element, said location pieces of thesurface element having outwardly faces.

8. A seal according to claim 1 wherein a channel or recess on one faceof the backing element provides a seat for the surface element.

9. A seal according to claim 1 wherein a coating of low-frictionmaterial is provided on the sealing face of the surface element.

10. A seal according to claim 1 wherein the backing element comprisesceramic fibers moulded together with a binding agent.

11. A seal comprising a composite of (a) a surface element having anexposed working face adapted to effect a sliding seal between it and anindependent cooperating member movable with respect thereto and (b) anintegral resilient support for resiliently supporting said surfaceelement and for providing a seal for the region enclosed thereby, saidresilient support being comprised of a fibrous backing elementpermanently attached to the opposite face of said surface element, saidbacking element being principally composed of low bulk density fibrousmaterials.

12. A seal comprising a composite of (a) a surface element having anexposed working face adapted to effect a sliding seal between it and anindependent cooperating member movable with respect thereto and (b) afibrous backing element secured to the opposite face of said surfaceelement, said backing element serving as a resilient support for saidsurface element and as a seal for the region enclosed thereby, thedensity of the backing element being varied with the distance from thesurface element, the region of greatest density being located closest tosaid surface element.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pater 1t No.3,633,926 Dated January 11, 1972 Inventor s Waldemar Hryniszak et a1 Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

On the cover sheet [73] the name of the Assignee should read CLARKECHAPMAN-JOEE! THOMPSON LIMITE Column 3, line 15, "internal" should readintegral Signed and sealed this 21st day of November 1972 (SEAL) Atteet:

EDWARD M.FLETCHER,JR. ROBERT GOT'ISCHALK Attesting Officer Commissionerof Patents FORM PO-1050 (10-69) USCOMM DC 5376 p69 us. eovzmmzu-rPRINTING OFFICE was O366-33I,

2. A seal according to claim 1 wherein the backing element has a densitythat varies with the distance from the surface element, the region ofgreatest density being closest to the surface element.
 3. A sealaccording to claim 1 wherein the surface element comprises a metalmember formed separately from the backing element.
 4. A seal accordingto claim 1 wherein auxiliary location pieces are provided on the surfaceelement, said pieces projecting away from the sealing face to engage thebacking element so as to prevent relative movement between the surfaceand backing elements in a plane parallel to the sealing face.
 5. A sealaccording to claim 4 wherein said location pieces lie on opposite sideedges of the backing element section, an inwardly directed lip on atleast one piece projecting into its associated backing element sideedge.
 6. A seal according to claim 4 wherein a housing or support meanscarries the surface and backing elements, said means having a sectionalwidth greater than the backing element, said location pieces of thesurface element having outwardly directed lips that increase the overallsectional width of the surface element substantially to that of thehousing or support means.
 7. A seal according to claim 6 wherein thehousing or support means is provided with opposed side surfaces thatextend towards the surface element to embrace at least a portion of thedepth of the backing element between them, said location pieces beingdisposed at spaced interruptions of said side surfaces.
 8. A sealaccording to claim 1 wherein a channel or recess on one face of thebacking element provides a seat for the surface element.
 9. A sealaccording to claim 1 wherein a coating of low-friction material isprovided on the sealing face of the surface element.
 10. A sealaccording to claim 1 wherein the backing element comprises ceramicfibers moulded together with a binding agent.
 11. A seal comprising acomposite of (a) a surface element having an exposed working faceadapted to effect a sliding seal between it and an independentcooperating member movable with respect thereto and (b) an integralresilient support for resiliently supporting said surface element andfor providing a seal for the region enclosed thereby, said resilientsupport being comprised of a fibrous backing element permanentlyattached to the opposite face of said surface element, said backingelement being principally composed of low bulk density fibrousmaterials.
 12. A seal comprising a composite of (a) a surface elementhaving an exposed working face adapted to effect a sliding seal betweenit and an independent cooperating member movable with respect theretoand (b) a fibrous backing element secured to the opposite face of saidsurface element, said backing element serving as a resilient support forsaid surface element and as a seal for the region enclosed thereby, thedensity of the backing element being varied with the distance from thesurface element, the region of greatest density being located closest tosaid surface element.